Pattern enhancement using a gas cluster ion beam

ABSTRACT

A method of processing a substrate includes loading the substrate on a substrate holder. The substrate includes a major surface and a feature disposed over the major surface. The feature has a first width along an etch direction. The method includes exposing portions of the major surface and changing the first width of the feature to a second width along the etch direction by etching a first portion of the sidewalls of the feature with a gas cluster ion beam oriented along a beam direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/018,741, filed on Sep. 11, 2020, which claims the benefit of U.S.Provisional Application No. 63/015,157, filed on Apr. 24, 2020, whichapplications are hereby incorporated herein by their reference.

TECHNICAL FIELD

The present invention relates generally to fabricating patterned layers,and, in particular embodiments, to pattern enhancement using a gascluster ion beam (GCIB).

BACKGROUND

Generally, a semiconductor device, such as an integrated circuit (IC) isfabricated by sequentially depositing and patterning layers ofdielectric, conductive, and semiconductor materials over a semiconductorsubstrate to form a network of electronic components and interconnectelements (e.g., transistors, resistors, capacitors, metal lines,contacts, and vias) integrated in a monolithic structure. At eachsuccessive technology node, the minimum feature sizes are shrunk toreduce cost by roughly doubling the component packing density.

A common patterning method is to use a photolithography process toexpose a coating of photoresist over the target layer to a pattern ofactinic radiation and then transfer the relief pattern to the targetlayer or an underlying hard mask layer formed over the target layer.With this technique, the minimum feature size for a manufacturableprocess would be limited by the resolution of the optical system. Deepultraviolet (DUV) 193 nm immersion photolithography systems can printfeature sizes down to about 40 nm. Sub-resolution features may be formedusing multiple patterning techniques. For example, with doublepatterning, DUV 193 nm immersion photolithography has been used tofabricate patterned layers at the 14 nm technology node with features atabout 38 nm pitch, but at a higher cost per wafer due to the extraprocessing steps used in multiple patterning. Further scaling of featuresizes for the 7 nm and 5 nm technology nodes may need 13.5 nm extremeultraviolet (EUV) photolithography. Stochastic effects resulting fromthe high energy of EUV photons exacerbate the line edge roughness (LER)and line width roughness (LWR) of photoresist patterns, making highfidelity pattern transfer a challenging task. Innovations may be neededthat enhance the pattern quality of patterned layers comprisingnanoscale features and lower the cost of patterning.

SUMMARY

In accordance with an embodiment of the present disclosure, a method ofprocessing a substrate includes loading the substrate on a substrateholder. The substrate includes a major surface and a feature disposedover the major surface. The feature has a first width along an etchdirection. The method includes exposing portions of the major surfaceand changing the first width of the feature to a second width along theetch direction by etching a first portion of the sidewalls of thefeature with a gas cluster ion beam oriented along a beam direction.

In accordance with an embodiment of the present disclosure, a method ofprocessing a substrate includes loading the substrate on a substrateholder, the substrate including a major surface and a plurality ofparallel lines disposed over the major surface; and exposing theplurality of parallel lines to a gas cluster ion beam oriented in a beamdirection, the beam direction having an orthogonal projection onto themajor surface, the orthogonal projection being oriented in an etchdirection, wherein the plurality of parallel lines are parallel with theetch direction.

In accordance with an embodiment of the present disclosure, a method ofprocessing a substrate includes loading the substrate on a substrateholder, the substrate including a major surface, a first featuredisposed over the major surface at a first location, and a secondfeature disposed over the major surface at a second location; exposingthe first feature to a first gas cluster ion beam with a first processparameter; and exposing the second feature to a second gas cluster ionbeam with a second process parameter, the first process parameter beingdifferent from the second process parameter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B illustrate planar views of a substrate at variousintermediate stages of a gas cluster ion beam pattern enhancementprocess, in accordance with an embodiment;

FIGS. 2A and 2B illustrate cross-sectional views of a substrate atvarious intermediate stages of the gas cluster ion beam patternenhancement process, shown in the planar views illustrated in FIGS. 1Aand 1B;

FIGS. 3A and 3B illustrate planar views of a substrate at variousintermediate stages of a gas cluster ion beam pattern enhancementprocess, in accordance with various embodiments;

FIGS. 3C and 3D illustrate the GCIB edge-displacement etch being used tochange the width of a construct within a patterned layer, wherein FIG.3C shows the gas cluster ion beam incident on the substrate tilted by atilt angle, and wherein FIG. 3D illustrates the patterned layer formedby exposing the initial pattern to the gas cluster ion beam;

FIG. 4 is a block diagram illustrating an execution flow for the gascluster ion beam pattern enhancement processes, shown in the planar andcross-sectional views illustrated in FIGS. 1A through 3B;

FIG. 5 illustrates cross-sectional views of a substrate at variousintermediate stages of three different options for a fabrication flow,each option comprising a gas cluster ion beam pattern enhancementprocess, in accordance with some embodiment;

FIG. 6 illustrates a perspective view of a desired patterned layercomprising parallel lines;

FIG. 7A illustrates a cross-sectional view of a substrate at anintermediate stage of a gas cluster ion beam pattern enhancementprocess, in accordance with an embodiment;

FIG. 7B illustrates a planar view of a substrate at an intermediatestage of the gas cluster ion beam pattern enhancement process, shown inthe cross-sectional view illustrated in FIG. 7A;

FIG. 8A illustrates a cross-sectional view of a substrate at anintermediate stage of a gas cluster ion beam pattern enhancementprocess, in accordance with an embodiment;

FIG. 8B illustrates a planar view of a substrate at an intermediatestage of the gas cluster ion beam pattern enhancement process, shown inthe cross-sectional view illustrated in FIG. 8A;

FIG. 9 is a block diagram illustrating an execution flow for the gascluster ion beam pattern enhancement process, shown in the planar andcross-sectional views illustrated in FIGS. 7A through 8B;

FIG. 10 illustrates a schematic of a substrate moved in a planar scanarea along a scan trajectory, in accordance with an embodiment;

FIG. 11 is a block diagram illustrating an execution flow for a locationspecific gas cluster ion beam pattern enhancement process, in accordancewith an embodiment;

FIG. 12A is a schematic of a gas cluster ion beam processing systemloaded with a substrate, in accordance with an embodiment;

FIG. 12B is a perspective view of the gas cluster ion beam processingsystem and substrate, shown in the schematic in FIG. 12A;

FIG. 13 illustrates a cross-sectional view of a scanning apparatusloaded with a substrate, in accordance with an embodiment; and

FIGS. 14A-14C illustrate schematics of a scanning apparatus loaded witha substrate rotated through various angles, in accordance with anembodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

This disclosure describes methods for enhancing a patterned layer bymaking fine adjustments to patterned features of the layer using a gascluster ion beam (GCIB). The disclosed processes may be advantageous forthe manufacturing of semiconductor integrated circuits that comprisepatterned layers designed using nanometer scale features by improvingpattern quality with minimal additional processing.

GCIB processing is a technique for controllable nanoscale processing ofa surface by exposing the surface to a highly collimated beam of highenergy clustered ions. Clusters of atoms or molecules of various sizes,loosely bound by van der Waals forces, may be formed by condensationinduced by adiabatic expansion of a gas; for example, by releasingcompressed gas (e.g., at about 10⁴ Torr) to a vacuum (e.g., about 10⁻²Torr) using a supersonic nozzle. A jet of nanometer size clustersemanating from the nozzle may pass through apertures into an ionizer inhigh vacuum (e.g., about 10⁻⁵ Torr) where the clusters are ionized bycolliding with energetic electrons to acquire an average positive chargeof a about +1e to +10e per cluster, where e is electron charge. The ionclusters may then be accelerated by a voltage drop of 10 kV to about 60kV, and collimated and directed by electromagnetic lenses to impinge onthe surface to be processed. The spot size of a gas cluster ion beam mayvary from a few microns to a few centimeters. In the embodiments of GCIBprocesses in this disclosure, the spot sizes may be about 1 cm to about10 cm in diameter. A Wien filter may be used to select a range ofcluster sizes; for example, from about 1000 atoms or molecules to about10,000 atoms or molecules. In various semiconductor processingapplications, the gas cluster ion beam may comprise inert gases such asnitrogen and argon, or reactants such as O₂, CO₂, NH₃, NF₃, SF₆, CF₄,CHF₃, or the like, or a mixture of several gases. Upon striking asurface, the cluster disintegrates and delivers most of its energytoward modifying the substrate physically and/or chemically. Althougheach cluster has high energy (e.g., about 30 keV to 80 keV), the energyper atom (or molecule) is low; the atoms (or molecules) are generallystopped within about a few nanometers (e.g., 10 nm to about 15 nm) fromthe surface. The cluster structure is thus exploited to deliver a highenergy density locally for close to ideal surface processing. Generally,a GCIB process may be performed with a total dose of about 10¹¹ clusterimpacts/cm² to about 10¹⁶ cluster impacts/cm². Furthermore, a low chargeto mass ratio of clusters allows for GCIB processing with a low beamcurrent (e.g., about 0.5 mA to about 0.15 mA). The low beam currentprovides the advantages of avoiding undesirable surface charging andsubstrate heating by keeping the average power to be less than about 1 Wto about 5 W for the embodiments described in this disclosure.

Embodiments of GCIB processes are disclosed that may be used to editfeatures within a patterned layer to provide feature sizes smaller thanthe resolution limit of the photolithography system used to form theinitial pattern. The sub-resolution features may be created bydisplacing the patterned edges of features with a gas cluster ion beam.The GCIB processes described in this disclosure provide the advantage ofprinting features with sub-resolution dimensions at a cost lower thanthe cost of using, for example, a litho-etch-litho-etch (LELE) doublepatterning technique. Example embodiments of methods for processing apatterned layer on a substrate to alter the shape of features within thepatterned layer is described in detail further below with reference toFIGS. 1A through 4 . Three different execution flow options using GCIBedge-displacement etch for obtaining the same target pattern in a targetlayer is illustrated below with reference to FIG. 5 .

Random variations in critical dimensions in a pattern result fromsurface roughness of sidewalls along the edges of features, such aslines, trenches, pillars, and holes within a patterned layer.Embodiments of GCIB processes will be described that enhance a patternedlayer by smoothing the surfaces of features by trimming randomprotrusions from exposed surfaces using a gas cluster ion beam. A GCIBtrim etch process may also be applied to descum a patterned layer.Example embodiments of GCIB trim etch processes are described in detailfurther below with reference to FIGS. 6 through 9 .

Methods to enhance a pattern by reducing variability of a criticaldimension using location specific edge-correction processing with a gascluster ion beam have been provided. Systematic variations in patterneddimensions from the respective target dimensions are often locationspecific. For example, a spatially nonuniform gas flow pattern of areactant gas in a process chamber during an etch process may cause acritical dimension in a patterned layer to be systematically larger thantarget, for example, in a region closer to the edge of the substrate. Inthe embodiments of location specific processing (LSP) methods describedin this disclosure, an adaptive GCIB process is used, wherein theprocess is dynamically altered in accordance with the location of thesubstrate as the substrate is moved through a gas cluster ion beam.Embodiments of GCIB-LSP techniques are described in detail further belowwith reference to FIGS. 10 and 11 .

The processing system, in which the GCIB processes described in thisdisclosure may be performed, comprises a processing chamber coupled to aGCIB source and a scanning apparatus. The processing may be controlledby, for example, a programmable electronic controller. An example of aGCIB processing system and various orientations in which the substratemay be positioned relative to the gas cluster ion beam are describedfurther below with reference to FIGS. 12A through 14C and is describedin further detail in U.S. Provisional Application No. 63/15,157.

FIG. 1A illustrates a planar view of a rectangular array of roughlycircular openings 100 having a width w in a patterned layer no. Thearray of circular openings 100 may be edited using a gas cluster ionbeam to form a respective array of roughly oval shaped openings 105,shown in FIG. 1B. The cross-sectional views, corresponding to the planarviews in FIGS. 1A and 1B, are shown in FIGS. 2A and 2B, respectively,along a cut-plane indicated by a dashed line A-A′ in FIGS. 1A and 1B. Asillustrated in FIG. 2A, the openings wo may be holes extendingvertically to expose portions of a roughly planar major surface of asubstrate 200 over which the patterned layer has been formed. Thepatterned layer no may comprise, for example, photoresist and thesubstrate 200 may comprise a layer of stacked layers, the major surfacebeing, for example, a top surface of a silicon-containing antireflectivecoating (SiARC).

In the figures in this disclosure, the x and y axes represent referencedirections in the plane of the substrate and the z-axis represent thenormal to the surface, also referred to as the major surface of thesubstrate. For the examples in this disclosure, the substrate 200 is asemiconductor substrate (e.g., a silicon substrate). The origin of thex-y-z rectangular system is selected to be at the center of the topsurface (the major surface) of the semiconductor substrate, and they-axis is selected to be a line going through the center and a notchmade in the initial semiconductor wafer over which the subsequent layersof the substrate 200 have been formed. The dimensions of patternedfeatures (e.g., the width w) are defined and measured in the x-y plane.The orientations of the patterned features, such as the orientation ofword lines relative to the orientation of bit lines in a memory array,also refer to the x and y axes. The substrate holder on which thesubstrate is loaded is in a plane parallel to the major surface of thesubstrate separated by the wafer thickness. During processing, thescanning apparatus of the GCIB system used in the embodiments in thisdisclosure moves the substrate and the substrate holder through a gascluster ion beam along a scan trajectory in the x-y plane, as describedin U.S. Provisional Application No. 63/15,157.

In the embodiments described in this disclosure, the gas cluster ionbeam of the GCIB processing system remains fixed while the substrate ismoved using a scanning apparatus. For specificity, consider a horizontalgas cluster ion beam oriented in a direction, referred to as the beamdirection. If the GCIB process is to be used to change the width of afeature then the major surface of the substrate has to be tiltedrelative to the beam direction; a vertically incident gas cluster ionbeam would not be effective in altering a dimension along a direction inthe plane of the major surface. Thus, prior to scanning through the gascluster ion beam, the scanning apparatus may adjust the orientation ofthe substrate relative to the gas cluster ion beam by rotating asubstrate holder on which the substrate is placed.

The tilt of the substrate is quantified by the angle between the z-axisand the beam direction, referred to as a tilt angle, θ, where verticalincidence is defined to be θ=0°. In this disclosure, the tilt angle (θ)is set by rotating the substrate holder (and the substrate) using acircular rotatable feedthrough connecting a scanner chamber and aprocess chamber, as described in U.S. Provisional Application No.63/15,157 and also further below with reference to FIG. 12B, FIG. 13 ,and FIGS. 14A-14C. The axis about which the substrate is rotated to setθ is the central axis of the circular rotatable feedthrough and isdesigned such that the axis of rotation is perpendicular to the beamdirection.

In the example illustrated in FIG. 2A, the substrate 200 has been tiltedrelative to the beam direction. Initially, the z-axis of the substrate200 may be in the direction of the dashed arrow. The gas cluster ionbeam (indicated by parallel arrows) would then be normal to the majorsurface of the substrate 200 (tilt angle=o °). A clockwise rotation ofthe substrate holder through an angle θ tilts the substrate 200 relativeto the beam direction. As illustrated in FIG. 2A, the rotation resultsin the normal to the surface (the z-axis indicated by the solid arrow)and the gas cluster ion beam to form an angle θ=0°. The gas cluster ionbeam now strikes one side and top surface of the patterned layer andstart removing material from these surfaces, thereby displacing the edgeof the etched sidewall along a direction in the x-y plane, referred toas the etch direction. In FIGS. 1A and 2A, the etch direction isindicated by wide arrows. As illustrated in FIG. 2A, the etch directionis the direction of the orthogonal projection of the beam direction ontothe tilted x-y plane. In FIG. 1A, the etch direction (or the orthogonalprojection of the beam direction) and the y-direction are coincident. Asexplained in U.S. Provisional Application No. 63/15,157 and also furtherbelow, the substrate may be rotated about the z-axis to adjust theangular position of the notch, thereby setting the y-direction asdesired.

The example embodiments use a minimum tilt angle of 10° and a maximumtilt angle of 85° (in either positive or negative directions) althoughthe scanning apparatus may rotate the substrate holder a tilt angle overa range −90°≤θ≤90°. One exemplary embodiment may use a minimum tiltangle of 10° and a maximum tilt angle of 65° (in either positive ornegative directions) although the scanning apparatus may rotate thesubstrate holder a tilt angle over a range −90°≤θ≤90°.

In FIGS. 1A and 2A, the patterned layer 110 comprising photoresist isbeing exposed to a gas cluster ion beam comprising oxygen clusters. Theopenings 100 are circular holes with a width w along the y-direction ofabout 10 nm to about 50 nm exposing a SiARC major surface of thesubstrate 200. Oxygen clusters may etch photoresist at the top surfaceand the exposed portions of the sidewalls of the openings 100 of thepatterned layer 110 with high selectivity to the SiARC major surface ofthe substrate 200. In this embodiment, the GCIB etch process may beprimarily a directional chemical etch, similar to a reactive ion etch(RIE) process. The etch rate is roughly directly proportional to theaverage flux density of reactants impinging on the surface, for example,the average number of oxygen cluster impacts per unit time per unit areaof the surface, in this example embodiment. Accordingly, the photoresistat the top surface would be etched at a rate roughly proportional to thez-component of the cluster-flux density of the gas cluster ion beam (or,∝ cos (θ)), while the etch rate at the sidewall (which is perpendicularto the top surface) would be roughly proportional to the orthogonalprojection of the cluster flux density onto the x-y plane (or, ∝ sin(θ)). For example, at vertical incidence, or θ=0°, sin (θ)=0; the etchrate at the sidewall is zero, but the top surface gets etched(cos(0°)=1). As θ is increased, the sidewalls etch at an increased rate,and the edge of the opening 100 may be displaced along the etchdirection (the direction parallel with the orthogonal projection of thegas cluster ion beam), which is the y-direction, in this example.

As mentioned above, the objective of the GCIB etch process in thisembodiment is to increase the width, w, of the circular openings 100 inthe patterned layer 110 (illustrated in FIG. 1A) by Δw along they-direction to form the patterned layer 115 comprising oval-shapedopenings 105 having a width (w+Δw) in the y-direction, as illustrated inFIG. 1B. In order to etch the sidewall uniformly from the top of theopening 100 to the bottom, the gas cluster ion beam has to access themajor surface at the bottom of the patterned layer 110 comprisingphotoresist of height, h, as illustrated in FIG. 2A. This constrains thetilt angle, θ, to the range 0<θ<tan⁻¹ (w/h), as may be seen from thecross-sectional view in FIG. 2A. Because the top surface is exposed,some photoresist is removed from the top surface. As illustrated in FIG.2B, at the completion of the GCIB etch process, the height of thepatterned layer 115 has reduced by an amount Δh. Loss of photoresistthickness limits its usefulness as an etch mask in a subsequent etchstep used transfer the pattern from the patterned layer 115 to anunderlying layer. In order to keep Δh small, a high tilt angle, θ, maybe selected for which the constraint 0<θ<tan⁻¹ (w/h) can be maintainedafter accounting for the process control capability of the scanningapparatus.

The GCIB etch removes a portion of the photoresist between adjacentopenings along the y-direction to form the stretched openings 105. Thisprocess simultaneously reduces the dimension of the photoresist betweenadjacent openings along the y-direction by Δw, as illustrated in FIGS.1B and 2B. In some embodiment, the reduced dimension, r, of thisphotoresist feature may be less than the resolution limit of thephotolithography system used to form the patterned layer no. The GCIBprocess used to form the sub-resolution features in the patterned layer115 provides the advantage of lower cost relative to using, for example,a more expensive double patterning technique, such as LELE, to form thefinal pattern 115.

In this example embodiment the patterned layer 100 is a patternedphotoresist layer but, it is understood that in various otherembodiments, the patterned layer 100 may be a hard mask layer such as,spin-on carbon, or silicon oxide, or silicon nitride, or titaniumnitride, or a metal, or a metal oxide, or a combination thereof. Severalsuch options are illustrated further below with reference to FIG. 5 .

Although the gas cluster ion beam is fixed, the directional GCIB etchmay be performed in any desired direction in the pattern by rotating thesubstrate 200, or equivalently, rotating the x-y axes about the z-axisby an angle, ϕ, referred to as the twist angle. For example, in FIGS. 3Aand 3B, substrate 200 has been rotated by (I)=45° relative to theorientation ϕ=0°, shown in FIGS. 1A and 1B. It is noted that theorientation ϕ=0° has been selected as the orientation for which they-axis is coincident with the etch direction (the direction along whichthe GCIB etch would be progressing). Since the direction of the gascluster ion beam is fixed, the etch direction is always the direction ofan orthogonal projection of the gas cluster ion beam onto the plane ofthe substrate. In FIGS. 3A and 3B, the substrate (and the pattern alongwith the substrate) has been rotated by ϕ=45°. Accordingly, the y-axis,as shown in FIGS. 3A and 3B, is no longer parallel with the etchdirection, indicated by a dashed line B-B′ in FIGS. 3A and 3B and thewide arrow in FIG. 3A. Instead, the y-axis and the line B-B′ form theangle, (I)=45°, as illustrated in FIGS. 3A and 3B. For ϕ=45°, thedistance between adjacent openings 100 along the direction of theprojected gas cluster ion beam in FIG. 3A is about 1.8×w if therespective distance in FIG. 1A is equal to the width of the openings, w.FIG. 3B illustrates the patterned layer 115 with the oval shapedopenings 105 after the GCIB etch process is completed. Exposure to thegas cluster ion beam changes the circular openings 100 of width, w, tothe oval shaped openings 105 of width (w+Δw) along the etch direction,indicated by a dashed line B-B′ that is shown forming an angle ϕ=45°with the y-axis in FIGS. 3A and 3B. Since the only difference betweenthe GCIB edge-displacement etch process in FIGS. 1A and 1B and the GCIBedge-displacement etch process in FIGS. 3A and 3B is the change in thetwist angle from ϕ=0° to ϕ=45°, the edge displacement, Δw, remains thesame.

FIGS. 3C and 3D illustrate the GCIB edge-displacement etch being used tochange the width of a construct within a patterned layer 330. Featuressuch as lines and pillars are referred to as constructs, whereastrenches and holes are referred to as openings. A construct in apatterned layer is separated from adjacent constructs by a cavity in thelayer. The previous two examples, illustrated using FIGS. 1A through 3B,were applications of a GCIB etch process used to elongate holes in twodifferent directions in a patterned array of circular holes. FIGS. 3Cand 3D illustrate the same GCIB etch process applied to shrink pillarsin a patterned layer 330 comprising an array of circular pillars spacedby cavities in the patterned layer such as cavity 300. FIG. 3C shows thegas cluster ion beam incident on the substrate 200 tilted by a tiltangle, θ. The pillars in the initial patterned layer 330 are of width w,and are spaced from adjacent pillars by a distance w along the etchdirection.

FIG. 3D illustrates the patterned layer 335 formed by exposing theinitial pattern 330 to the gas cluster ion beam. In FIG. 3D, the initialwidth w of the pillars is reduced by a length, Δw, along the etchdirection. The respective space between adjacent pillars, which is thecavity 305, is wider than the initial cavity 300 by the same length, Δw.

In the above examples of the edge-displacement etches, the width of afeature has been adjusted by etching in a direction defined by a firsttwist angle, ϕ₁. However, it is understood that in other embodiments thewidth of the same feature may be adjusted from the opposite direction.The etching in the opposite direction is performing the same etchprocess, but selecting a second twist angle, ϕ₂, where ϕ₂=ϕ₁+180°. Boththe GCIB etches may be performed successively on the same substrate, andthe respective adjustments, Δw, to the width, w, may be selected to bedifferent, for example, by selecting different GCIB exposure doses.

FIG. 4 is a block diagram for the execution flow 400 used to performGCIB edge-displacement etches, such as those described above withreference to FIGS. 1A through 3B.

As indicated in block 410, in the execution flow 400, the substrate(e.g., substrate 200) is loaded on a substrate holder of a scanningapparatus. The incoming substrate has a feature such as lines, pillars,holes, or trenches, formed in a patterned layer (e.g., the photoresistpatterned layer no) disposed over a major surface (e.g., the majorsurface of the substrate 200 comprising SiARC). The feature, (e.g., theopenings 100) has a first width, w, along an etch direction. Portions ofthe major surface over which the patterned layer is disposed may beexposed.

A GCIB etch process may be used to change the width of the feature fromthe first width, w, to a second width along the first direction, asindicated by block 450 in FIG. 4 . Prior to etching, the substrate ispositioned to a desired orientation relative to the gas cluster ion beamusing the scanning apparatus, as indicated in block 420 of the executionflow 400. Orienting the substrate comprises tilting the substrate (box422) relative to the direction of the gas cluster ion beam and rotatingthe substrate (box 424) about the central axis (z-axis) normal to themajor surface (the x-y plane). The tilt angle (θ) may be selected to beas close to a right angle as possible, subject to a constraint thathelps avoid partial exposure of a sidewall along its height, asdescribed above with reference to FIG. 2A. The rotation about thecentral axis may be performed through a twist angle selected to alignthe direction along which the width may be changed (the etch direction)to be parallel with a desired direction in the pattern. The twist angle(ϕ) is defined with respect to a reference axis (the y-axis) in theplane of the major surface, as described above.

Once the substrate is oriented, it may be actively maintained at theselected orientation by the scanning apparatus for the duration of theprocess, as indicated in block 430.

In block 440 of the execution flow 400, the width of the feature ischanged by an edge-displacement GCIB etch process that is used tore-position the sidewalls of the features in the patterned layer. Thescanning apparatus moves the substrate through the gas cluster ion beam,thereby exposing a target area of the substrate to a target dose ofcluster impacts. Exposure to the target dose of cluster impactsdisplaces the exposed sidewalls along the first direction. Clustersimpinging on an exposed surface may remove material from the surfacephysically and chemically. In order to achieve the desired edgedisplacement without damaging the exposed portions of the major surface,the gases used by the GCIB source to form gas clusters comprise chemicaletchants that may selectively remove the sidewall material at a fasterremoval rate relative to the respective removal rate of the material ofthe exposed major surface.

Although, in the execution flow 400, as well in other execution flowsreferred to in this disclosure to describe GCIB processes, the substrateorientation is selected by the scanning apparatus, in some otherembodiment, the substrate may be oriented using a separate aligningmechanism. For example, an initial alignment to select an initial twistangle may be done using a separate substrate aligner (separate from thescanning apparatus) in the substrate transport path through which thesubstrate may be transported from outside the scanning apparatus to thesubstrate holder of the scanning apparatus. It is noted that, asdescribed in U.S. Provisional Application No. 63/15,157, duringscanning, the orientation of the wafer may have to be adjusted activelyby rotation about the z-axis to maintain a constant twist angle inaccordance with the (x, y) coordinates of the wafer.

FIG. 5 illustrates an example of patterning a target layer 525 in anincoming substrate comprising a stack of layers, the topmost layer beinga patterned layer 500 formed by transferring a radiation pattern onto aphotoresist film. The description for the stack of layers of theincoming substrate in this example includes specific materials for thepurpose of illustration, and should not be construed to be limiting.

Three different fabrication flow options have been illustrated in FIG. 5, each of which comprises a GCIB edge-displacement etch process step533, indicated by an open arrow. For each of the options, the processingsequence is indicated by solid arrows between cross-sectional views ofthe substrate at various intermediate stages of fabrication.

All the three options in FIG. 5 use the same incoming substrate, havinga top patterned layer 500 comprising an EUV photoresist. All threeoptions use the same pattern of openings 550 of width, w, formed in theEUV photoresist. In all three options, trenches are patterned in thetarget layer 525 comprising a low dielectric constant (low-k) interlayerdielectric (ILD) such as fluorosilicate glass (FSG) or carbon-dopedoxide (CDO). At the completion of each of the three fabrication flows,the patterned ILD layer 526 comprises trenches 556 having a width(w+Δw). For all three fabrication flow options, at some point in asequence of processing steps, a GCIB edge-displacement etch process step533 has been inserted. The GCIB process step 533 may edit the exposedpattern to change the width dimension from w to (w+Δw) by exposing thesubstrate to a gas cluster ion beam.

The three fabrication flows differ in the position where the GCIBprocess step 533 is inserted in the sequence of pattern-transfer andlayer-strip etches performed to process a stack of four layers betweenthe top patterned layer 500 and the target ILD layer 525 of the incomingsubstrate. The cross-sectional view of the substrate after the GCIBprocess step 533 is completed is indicated by an open arrow. The edgedisplacement (Δw) and the thickness reduction in the edited patternedlayer are highlighted by a dashed outline of the surfaces of therespective initial pattern.

As illustrated in FIG. 5 , the stack of four layers between the toppatterned layer 500 and the target ILD layer 525 comprises a SiARC layer505, shown underlying the photoresist patterned layer 500, followed by astack of three hard mask layers. Adjacent to the SiARC layer 505 is afirst hard mask layer 510 comprising spin-on carbon. A silicon dioxidesecond hard mask layer 515 may be an etch stop for a pattern-transferetch that may be used to pattern the carbon first hard mask layer 510.The third hard mask layer 520 comprising titanium nitride is disposedadjacent to the low-k ILD layer 525. The titanium nitride third hardmask layer 520, or the titanium nitride third hard mask layer 520 inconjunction with the silicon dioxide cap (second hard mask layer 515)may be patterned and used as the hard mask for the finalpattern-transfer etch used to pattern the ILD layer 525 to form thetrenches 556 in the patterned ILD layer 526.

The sequence of pattern-transfer and layer-strip etches performedcomprises a first pattern-transfer etch using an EUV photoresist mask toetch the SiARC layer. A second pattern-transfer etch may use thepatterned SiARC as a hard mask to transfer the pattern to the carbonhard mask layer, stopping the etching on the silicon dioxide layer. TheSiARC may be stripped prior to using the patterned carbon as the hardmask to pattern the underlying silicon dioxide and titanium nitridelayers. Another layer-strip etch may be used to remove the carbon hardmask layer before the final pattern-transfer etch is performed to etchtrenches in the ILD layer using the silicon dioxide and titanium nitridebilayer hard mask. The silicon dioxide and the titanium nitride layersremaining at the end of the etching may be stripped to form the finalpatterned ILD layer.

In the first fabrication flow, Option A, the GCIB edge-displacement etchprocess step 533 is inserted in the beginning of the fabrication flow.As illustrated in FIG. 5 , the GCIB process step 533 of Option A maychange the width, w, of the opening 550 to form a wider opening 551 ofwidth (w+Δw) in the edited EUV photoresist patterned layer 501. Theedited patterned layer 501 is used as a mask to etch the underlyingSiARC layer 505, and the rest of the sequence of pattern-transfer andlayer-strip etches may be performed in the usual way, as describedabove.

In the second fabrication flow, Option B, the EUV photoresist patternedlayer 500 of the incoming substrate is used as a masking layer to etchthe SiARC to form the patterned SiARC layer 506. The pattern may betransferred further down to etch the first carbon hard mask layer 510 toform the openings 552 in the patterned carbon hard mask layer 511. InOption B, the GCIB edge-displacement etch process step 533 is insertedafter the SiARC strip to edit the patterned carbon hard mask layer 511.As illustrated in FIG. 5 , the GCIB process step of Option B may changethe width of the opening 552 to form a wider opening 553 of width (w+Δw)in the edited patterned carbon hard mask layer 512. The edited patternedcarbon hard mask layer 512 may be used as a mask to etch the underlyingsilicon dioxide second hard mask layer 515 and the titanium nitridethird hard mask layer 520. The rest of the sequence of pattern-transferand layer-strip etches may be performed in the usual way, as describedabove.

Oxygen can be used as an etchant to remove EUV photoresist selective toSiARC, and also as an etchant to remove spin-on carbon selective tosilicon dioxide. Accordingly, a gas cluster ion beam comprising oxygenclusters may be used to perform the GCIB edge-displacement etch processsteps in the first fabrication flow (Option A) and the secondfabrication flow (Option B).

In the third fabrication flow, Option C, illustrated in FIG. 5 , theusual sequence of processing steps, described above, is performed totransfer the pattern of the incoming EUV patterned layer 500 to form theopenings 552 in the patterned carbon hard mask layer 511, and use thecarbon hard mask layer 511 to pattern the second and third hard masklayers 515 and 520. As illustrated in FIG. 5 , in Option C, the abovesequence of processing steps forms the openings 554 having a width, w,in the patterned bilayer hard mask comprising the patterned silicondioxide hard mask layer 516 and the patterned titanium nitride hard masklayer 521. The GCIB edge-displacement etch process step 533 is insertedat this position in the processing sequence of the third fabricationflow (Option C) to widen the opening 554. The opening 555, in the editedbilayer hard mask comprising the silicon dioxide hard mask layer 517 andthe titanium nitride hard mask layer 522, has been widened from w to(w+Δw). Accordingly, after the final pattern-transfer etch is completed,the respective opening 556 in the patterned ILD layer 526 is also(w+Δw).

The gas cluster ion beam used for the GCIB edge-displacement etchprocess step 533 of Option C comprises NF₃ clusters since NF₃ can etchsilicon dioxide and TiN selective to the low-k ILD. In this case, anadditional layer such as aluminum nitride protects the target ILD layer525 during the GCIB edge-displacement etch process step 533. Theadditional layer is subsequently removed.

For all three options, at the end of the sequence of process steps, theILD layer 525 has been patterned forming a pattern of trenches 556having the desired elongated width (w+Δw) in the patterned ILD layer526.

It is generally desirable to have smooth surfaces of features in apatterned layer. One consequence of surface roughness is randomvariation in linewidth that may, in turn, cause random variations in theelectrical properties of devices. For example, random variation in thegate length of minimum gate length transistors may result in anexponentially amplified variation in transistor subthreshold leakage.Likewise, the electrical resistances of minimum width interconnect linesmay be very sensitive to linewidth variations. In various instances,forming smoother surfaces during patterning reduces electricalvariability of circuit elements fabricated using the patterned layer.However, the patterning process may not yield the desired smoothness.For example, it is noted that photoresist lines patterned using an EUVphotolithography system exhibit relatively high LER and LWR due tostochastic effects resulting from the high energy of EUV photons, asknown to persons skilled in the art. As mentioned above, GCIB trim etchprocesses may be used to smooth rough surfaces. An example embodimentwhere a GCIB trim etch process has been applied to smooth the surfacesof a patterned photoresist layer is described with reference to FIGS. 6,7A-7B, and 8A-8B. The method is illustrated using a block diagram shownin FIG. 9 .

FIG. 6 illustrates a perspective view of an example of a desiredpatterned layer comprising an array of parallel lines 640 formed over amajor surface 606 of a substrate. Disposed between adjacent parallellines 640 is a gap region 650. The pattern of parallel lines 640 withmore realistically rough surfaces is shown in a cross-sectional view inFIG. 7A and in the respective top planar view in FIG. 7B. The sidewallsand the top surfaces, illustrated in the views in FIGS. 7A and 7B, arerough relative to the desired smooth surfaces of the parallel lines 640illustrated in FIG. 6 .

In addition to the more realistic surface roughness, a photoresistresidue 636 may be adhering to the major surface 606 in the gap region650, as illustrated in FIGS. 7A and 7B.

In this example, the patterned layer of parallel lines 640 comprises anEUV photoresist and the major surface 606 of the substrate comprises aSiARC. It is understood that the innovative aspects of the describedembodiment are applicable to other embodiments using other materials.

In FIGS. 8A and 8B, a GCIB trim etch process has been performed. FIG. 8Aillustrates the cross-sectional view of the structure in FIG. 7A, andFIG. 8B illustrates the respective top planar view. As illustrated inFIGS. 8A and 8B, the surfaces of the photoresist parallel lines 640 havethe desired smoothness. Furthermore, the GCIB trim etch process hasdescummed the pattern by removing the photoresist residue 636 from theSiARC major surface 606.

An execution flow 900 for performing a GCIB trim etch process isillustrated in the block diagram in FIG. 9 . Referring to FIG. 9 , theexecution of GCIB trim etch processing commences with loading anincoming substrate on a substrate holder of a scanning apparatus, asindicated in block 910 of the execution flow 900. The incomingsubstrate, in this example, comprises a major surface (e.g., majorsurface 606) and a plurality of parallel lines (e.g., parallel lines640) disposed over the major surface.

The plurality of parallel lines may be exposed to a gas cluster ion beamin order to smooth the surfaces of the parallel lines, and also todescum the parallel lines by removing residues of EUV photoresist on themajor surface, as indicated by block 920 of the execution flow 900.Exposing the parallel lines may involve executing several actions:orienting the substrate relative to the gas cluster ion beam (box 925),maintaining the substrate at the selected orientation (box 935),selecting a set of gas cluster ion beam parameters (box 945), and movingthe substrate through the gas cluster ion beam using the scanningapparatus.

The gas cluster ion beam is in a fixed direction, referred to here asthe beam direction, and its orthogonal projection onto the major surfacemay be referred to as the etch direction. Note that, in the context of aGCIB trim etch process, the term etch direction is not the direction inwhich a dimension of a feature is being changed. In contrast to a GCIBedge-displacement process, the GCIB trim etch process is not intended tomodify the dimension of a feature. The GCIB trim etch process may beused to smooth surfaces by etching protrusions or reduce defects byetching residues (e.g., photoresist residue). The orientation of thesubstrate may be adjusted relative to the gas cluster ion beam (box 925of block 920). The substrate may be tilted to a tilt angle (θ) selectedto be as close to a right angle as possible within constraints (box921), as discussed above with reference to FIG. 2A. In variousembodiments, θ may be about 55° to about 85°, depending on thecapability of the scanning apparatus and tilt angle control. Inaddition, the substrate may be rotated about an axis normal to the majorsurface by a twist angle. The twist angle (ϕ) is selected to align theparallel lines to be parallel with the etch direction (box 923).

At this orientation of the parallel lines, the clusters in the gascluster ion beam are likely to collide with random photoresistprotrusions from the top surface and from the sidewalls into the gapregion between adjacent lines while having negligible effect on thedimensions of the patterned photoresist layer. Because the gas clusterion beam etches sidewalls primarily in a direction parallel with theetch direction, the edge displacement would be minimal with the parallellines oriented parallel with the etch direction. The high tilt anglewould also reduce the photoresist loss from the top surfaces of theparallel lines, as explained above with reference to FIG. 2A.

The relatively loosely bound clusters disintegrate upon impact with thephotoresist protruding from the surfaces of the parallel lines. Thelarge number of constituent atoms/molecules from a disintegratingcluster may be scattered in various directions analogous to mudsplattering on an automobile windshield. This provides a lateralsputtering effect which further assists in smoothing the photoresistlines. Since only a small amount of material removal is involved forsmoothing, the GCIB trim etch is generally performed using a low dose ofcluster impacts. As indicated in box 945 of block 920, a dose of about10¹¹ cluster impacts per cm² to about 10¹⁶ cluster impacts per cm₂ maybe selected in various embodiments. The gas cluster ion beam maycomprise, for example, oxygen clusters to etch photoresist selective tothe SiARC major surface or a mixture of argon and oxygen.

In addition to enhancing patterns by reducing random variations in acritical dimension such as LER and LWR, the GCIB etch technique may beapplied to reduce systematic variations in a critical dimension by usinglocation specific processing (LSP). As mentioned above, in an LSPmethod, the process is dynamically altered during processing inaccordance with the location of the substrate. This may be achieved byvarying an adjustable process parameter while the substrate is movedalong a scan trajectory. The adjustable process parameter is referred toas a control parameter.

A location specific etch may be performed using a GCIB-LSPedge-displacement etch process in which, for example, the total dose ofcluster impacts/cm² of the gas cluster ion beam is used as the controlparameter to provide a location specific edge displacement. The edgedisplacement also depends on other process parameters that may beselected to be a control parameter, for example, tilt angle and dwelltime. The dwell time may be defined as the local exposure time per unitarea. The twist angle may also be a control parameter if the directionof the etch needs to be location specific. The control parameter maycomprise any set of adjustable process parameters that may alter thepattern metric that is being changed to enhance the pattern quality. Thevalues of the components of the set would then collectively be referredto as the value of the control parameter.

Consider, for example, that it is known from measurements that thelinewidth of a feature is bigger than its target value by an amount thatincreases progressively with increasing radial distance of the locationof the features from the center to the edge of the substrate. If thelocation specific linewidth data is also provided, then this informationmay be utilized to design, for example, a GCIB-LSP edge-displacementetch, to reduce the linewidth errors. For example, the total dose ofcluster impacts/cm² may be increased as the location of the center ofthe substrate approaches the gas cluster ion beam and vice versa. Thelocation specific linewidth errors may be calculated from the locationspecific linewidth data and transformed to location specific values ofthe total dose of cluster impacts/cm² using a known relationship betweenedge displacement and the total dose of cluster impacts/cm² obtained apriori from process characterization data. Once the location specificcontrol parameter values are calculated, the substrate may be movedalong a selected scan trajectory by a scanning apparatus and the controlparameter may be adjusted by a controller, in accordance with thelocation specific calculated values.

FIG. 10 illustrates an example of a substrate 1000 being moved in aplanar scan area 1010 along a scan trajectory 1020 through a gas clusterion beam 1030. The scan trajectory 1020, in FIG. 10 , is a horizontalraster starting at the top left of the scan area 1010 and comprises afamily of horizontal traces indexed to cover the scan area fromtop-to-bottom. The scan area has an extra width margin which may be usedto ramp up the wafer velocity from zero at the beginning of a trace andramp it down to zero before the return trace. After indexing down to thebottom of the scan area, a return scan may be initiated. The scans arerepeated till the GCIB process is complete. A GCIB processing systemthat may perform the process is illustrated further below with referenceto FIGS. 12, 13, and 14A-C. The in-plane motion may be synchronized withthe angular orientation by active control and synchronized rotaryactuators, as mentioned below with reference to FIGS. 12A, 12B, and 13 ,and described in detail in the U.S. Provisional Application No.63/15,157.

FIG. 11 illustrates a block diagram for a GCIB-LSP process executionflow 1100 that may be used for pattern enhancement by achieving, forexample, reduced variability in a critical dimension with locationspecific error correction.

In block 1110, a substrate comprising a patterned layer formed over amajor surface is loaded on a substrate holder of a scanning apparatus.Consider a first feature in the patterned layer disposed at a firstlocation, and a second feature disposed at a second location over themajor surface. Location specific processing is achieved by exposing thefirst feature to a first gas cluster ion beam that processes the featureaccording to a first process parameter, and exposing the second featureto a second gas cluster ion beam that processes the feature according toa second process parameter, as indicated by block 1120 of the GCIB-LSPprocess execution flow 1100. Selecting the first process parameterdifferent from the second process parameter results in location specificprocessing of the features by the gas cluster ion beam.

The first process parameter and the second process parameter are twovalues of a control process parameter. For example, the first processparameter and the second process parameter may be two different totalcluster doses selected to provide the two desired edge displacements atthe two respective locations. In order to expose the first feature andthe second feature to the gas cluster ion beam, involves executing aseries of actions that comprises selecting a scan trajectory (box 1130)that includes the locations of the features, calculating the values ofthe control process parameter (block 1140) as a function of location ofthe substrate along the scan trajectory, moving the substratecontinuously along the scan trajectory using a scanning apparatus (box1150), and changing the process along the scan trajectory by selectingthe location specific value of the control process parameter to be sameas the respective calculated value (box 1160). For example, the value ofthe control process parameter at the first location is equal to thefirst process parameter, and the value of the control process parameterat the second location is equal to the second process parameter.

In order to appropriately calculate the values of the control processparameter as a function of location of the substrate along the scantrajectory the GCIB processing system has to receive some informationabout the incoming substrate and the GCIB etch process. The receivedinformation comprises the location specific data of a metric of thefeature (e.g., the linewidth data across various locations of the majorsurface), as indicated in box 1142, and the function relating the metricto a value of the control process parameter (box 1144), for example,process characterization data relating the total cluster dose to theedge displacement. As indicated in box 1146, the location specific datamay be used to calculate the edge displacement desired at each location,and the function may be used in calculating the respective value of thecontrol parameter, for example, the total cluster dose per unit area atthe respective location.

In the execution flow 1100, the corrections are performed while thewafer is moved once along a single trajectory. However, it is understoodthat in some other embodiment a first scan may be performed with a firsttwist angle, ϕ₁, to make edge corrections in one direction, and a secondscan may be performed with a second twist angle, ϕ₂, to make edgecorrections in the opposite direction. The corrections in the oppositedirection may be performed by selecting ϕ₂=ϕ₁+180°. Both the correctionsmay be performed successively on the same substrate.

Although we have described GCIB-LSP processing for error correction, theGCIB-LSP technique may also be applied to implement fabricating afeature with different target values, such as one target value forfeatures in a region within a particular radius from the centersubstrate, and a second target value for features in a region beyond aparticular radius from the center substrate. The variable may be adimension such as a width. The variable may also be a direction such asthe direction of the major axis of oval shaped holes in an array ofholes.

FIGS. 12A and 12B illustrate an example GCIB gas cluster ion beamprocessing system comprising a scanning apparatus 1200 coupled to aprocess chamber 1210, a GCIB source 1250 (partially behind the processchamber 1210 in FIG. 12A), and a controller 1260, for example, anelectronic programmable controller that may control the scanningapparatus 1200 and the GCIB source 1250. The scanning apparatus andmethod are described in detail in U.S. Provisional Application No.63/15,157. A substrate holder 1220 loaded with a substrate 1240 is showndisposed inside the process chamber 1210. The plane of the substrateholder 1220 is parallel with the plane of the major surface of thesubstrate 1240. The substrate holder 1220 is attached at the end of abar link 1222 of the scanning apparatus 1200 that extends into theprocess chamber 1210 through a rotatable feedthrough 1215. One side ofthe rotatable feedthrough 1215 is rigidly attached to a vertical wall1211 of the process chamber 1210. The opposite side may be rotatedrelative the side attached to the wall of the process chamber 1210. Thisrotatable side is attached to a scanner chamber 1224 which housesseveral bar links, hinges, and rotary actuators. Thus, the rotatablefeedthrough 1215 may rotate the entire scanner chamber 1224 about anaxis normal to the wall of the process chamber 1210, as seen in aperspective view illustrated in FIG. 12B.

The perspective view of the GCIB system in FIG. 12B illustrates the GCIBsource 1250 coupled to the process chamber 1210. A gas cluster ion beammay pass through an aperture 1252 toward the substrate holder 1220inside the process chamber 1210. The direction of the gas cluster ionbeam is fixed. The scanning apparatus 1200 may tilt the substrate holder1220 (and the substrate 1240) relative to the gas cluster ion beam,rotate the plane of the major surface, and move the substrate holder1220 (and the substrate 1240) along an in-plane scan trajectory toexpose the substrate 1240 to the gas cluster ion beam. The scantrajectory is in a plane, referred to as the scanning plane. Thescanning apparatus 1200 is designed to maintain the scanning planeroughly in parallel with the major surface of the substrate 1240.

FIG. 13 illustrates a cross-sectional view of the scanning apparatus1200 used to describe selection of an orientation of the substrate 1240relative to the gas cluster ion beam. The wall 1211 to which therotatable feedthrough 1215 is affixed is indicated by a dot-dash line;the rest of the process chamber 1210 is omitted for clarity. The scannerchamber 1224 attaches to the rotatable side, as described above. A pairof parallel dashed lines in bar link 1222 represents a motorizedbelt-and-pulley system connected between a rotary hinge and thesubstrate holder 1220 of the scanning apparatus 1200.

Generally, a substrate comprises a stack of patterned layers. Thepatterns are aligned to each other and to a reference direction in theplane of a major surface of the substrate. The notch in the majorsurface of the substrate 1240 in FIG. 13 defines the reference directionin the plane of the major surface. For example, the direction of theline connecting the notch and the center of the substrate may beselected as the reference axis, referred to as the y-axis. The y-axesand the orthogonal x-axis (indicated by two dashed arrows in FIG. 13 )define the plane of the major surface of the substrate 1240.

The reference y-axis may be rotated through an angle, ϕ, by rotating thesubstrate holder 1220 (and the substrate 1240) about a central axisnormal to the x-y plane (not visible here, but shown as the z-axis inFIGS. 14A-14C). The angle, ϕ, is referred to as the twist angle. Theorientation of the substrate 1240 in FIG. 13 depicts an orientationwhere ϕ=0°. The ϕ=0° orientation is defined here in reference to theplane of the wall 1211 of the process chamber 1210. At ϕ=0°, the y-axisis parallel with, and the x-axis is normal to the plane of the wall1211. At this orientation, an orthogonal projection of the gas clusterion beam onto the x-y plane would be parallel with the y-axis. Thiswould be illustrated in further detail in FIGS. 14A-14C. The rotation ofthe plane of the major surface of the substrate 1240 and substrateholder 1220 (the x-y plane), is indicated by an arc-shaped arrow nearthe notch. Rotating the substrate 1240 (or changing ϕ) alters theorientation of the features in a patterned layer relative to the gascluster ion beam. For example, if at ϕ=0°, the in-plane component of agas cluster ion beam is parallel with a line in the y-direction then atϕ=90°, the same gas cluster ion beam would have an in-plane componentintersecting the same line perpendicularly. The twist angle, ϕ, may beselected by rotating the substrate holder 1220 using a motorizedbelt-and-pulley system embedded in the bar link 1222 to which thesubstrate holder 1220 is attached. In the example scanning apparatus1200, the motorized belt-and-pulley system in the bar link 1222 may alsobe used synchronously with the rotary actuators to maintain a constant ϕwhen the substrate 1240 is moved along a scan trajectory in the x-yplane. The rotary actuators that move the wafer 1240 in the scanningplane are synchronized with each other and are also synchronized withthe motorized belt-and-pulley system in the bar link 1222 by thecontroller 1260 to actively maintain the angular orientation of thewafer 1240 (the twist angle) constant synchronously with the in-planemotion along the selected scan trajectory.

As mentioned above with reference to FIG. 12B, the rotatable feedthrough1215 may rotate the entire scanner chamber 1224 about an axis normal tothe wall 1211 of the process chamber 1210. In FIG. 13 , this isindicated by a broad open curled arrow. A rotation of the x-y planethrough an angle, θ, would tilt the substrate 1240 relative to the gascluster ion beam by a tilt angle, θ. The θ=0° orientation is definedhere in reference to the direction of the gas cluster ion beam. At θ=0°,the gas cluster ion beam is normal to the x-y plane (also the plane ofthe major surface of the substrate 1240). The tilt angle is explainedfurther with reference to FIGS. 14A-14C.

FIGS. 14A-14C show schematics of the scanning apparatus 1200 loaded witha substrate 1240. In FIGS. 14A-14C, the substrate holder 1220 andsubstrate 1240 are shown oriented at three different values of the tiltangle, θ. The tilt angle, θ, may be selected using the rotatablefeedthrough 1215 of the scanning apparatus 1200, as described above andindicated by a curved double arrow in FIGS. 14A-14C. A checkerboardpattern and a wafer notch marked on the major surface of the substrate1240 indicate that the twist angle, ϕ=0° in all three cases illustratedin FIGS. 14A-14C. The long cylindrical rod represents a gas cluster ionbeam 1400 incident on the substrate 1240 along a fixed direction,referred to as the beam direction and indicated by a dashed line passingthrough the gas cluster ion beam 1400.

In FIG. 14A, the gas cluster ion beam 1400 is perpendicular to (θ=0°)the major surface (the x-y plane) of the substrate 1240. Accordingly,the normal to the major surface (the z-axis) is coincident with the gascluster ion beam 1400.

In FIG. 14B, the rotatable feedthrough 1215 has been rotated through anangle, θ, thereby tilting the substrate by a tilt angle, θ, as describedabove. Accordingly, the normal to the major surface (the z-axis) formsan angle, θ, with the gas cluster ion beam 1400. It may be noted that,since ϕ=0°, the etch direction (defined as the direction of theprojection of the gas cluster ion beam 1400 onto the x-y plane) would beparallel with the y-axis. The beam direction and the etch direction arelabeled in FIG. 14B.

In FIG. 14C, the gas cluster ion beam 1400 is parallel with (θ=90°) themajor surface (the x-y plane) of the substrate 1240. Accordingly, thenormal to the major surface (the z-axis) is perpendicular to the gascluster ion beam 1400.

In this disclosure we have described embodiments of methods to enhancepatterns using GCIB processes performed using a GCIB system. Thedescribed embodiments may provide several advantages. The GCIBedge-displacement etch processes may be used to edit patterned layers tocreate, for example, sub-resolution features at a relatively low cost.The embodiments of GCIB trim etch processes, described herein, provideseveral advantages. A GCIB trim etch may be applied to removing etchresidue (e.g., descumming a photoresist pattern) and to smoothensurfaces. Smoothening sidewalls of features in a patterned layerenhances a pattern by reducing random electrical variations resultingfrom LER and LWR. Another technique utilizing GCIB processing are theembodiments of GCIB-LSP described in this disclosure. GCIB-LSP mayprovide the advantages of correcting CD variations using priorinformation of location specific measurements of the incoming substratesand GCIB process characterization data. The location specific etchcapability provided by the GCIB-LSP technique may also enablefabrication of a plurality of IC designs on the same substrate, whereeach design uses a different target value for a CD at some patternlevel.

Example 1. A method of processing a substrate includes loading thesubstrate on a substrate holder. The substrate includes a major surfaceand a feature disposed over the major surface. The feature has a firstwidth along an etch direction. The method includes exposing portions ofthe major surface and changing the first width of the feature to asecond width along the etch direction by etching a first portion of thesidewalls of the feature with a gas cluster ion beam oriented along abeam direction.

Example 2. The method of example 1, wherein the etch direction is alongthe orthogonal projection of the beam direction on the major surface sothat the gas cluster ion beam is inclined at a tilt angle with a normalto the major surface or the etch direction is parallel to the majorsurface and perpendicular to the sidewalls.

Example 3. The method of example 1, wherein the substrate is oriented ina first orientation relative to the etch direction while changing thefirst width. The method further includes rotating the substrate to asecond orientation relative to the etch direction, and changing thesecond width of the feature to a third width along the etch direction byetching a second portion of the sidewalls of the feature with the gascluster ion beam oriented along the beam direction.

Example 4. The method of example 3, wherein the rotating the substrateto the second orientation relative to the etch direction is performed bythe scanning apparatus or a separate aligning mechanism.

Example 5. The method of example 3, wherein the difference between thefirst width and the second width is different from the differencebetween the second width and the third width.

Example 6. The method of example 1, further including: loading thesubstrate on the substrate holder of a scanning apparatus; andorienting, using the scanning apparatus, the substrate relative to thegas cluster ion beam by tilting the substrate at a selected tilt angle,the tilt angle being the angle formed by the gas cluster ion beam and aline normal to the major surface; and rotating the substrate about anaxis normal to the major surface, wherein the rotation orients areference axis in the major surface to form a selected twist anglebetween the reference axis and a line parallel with the etch direction.

Example 7. The method of example 1, further includes orienting thesubstrate relative to the gas cluster ion beam while loading thesubstrate using a substrate aligner separate from the scanningapparatus.

Example 8. The method of example 6, wherein the tilt angle is selectedfor the gas cluster ion beam to impinge on a boundary between theexposed portion of the major surface and a sidewall of the feature, andwherein the tilt angle is selected to reduce the difference between thetilt angle and a right angle.

Example 9. The method of example 1, wherein the feature is within apatterned first layer that is disposed over the major surface and themajor surface including a second layer. The first layer includes a firstmaterial and the second layer includes a second material. In the method,changing the width of the feature along the etch direction includesmaintaining the substrate at a fixed orientation relative to the gascluster ion beam; exposing a target area of the substrate to a targetdose of cluster impacts by moving the substrate through the gas clusterion beam; and removing the first material at a faster removal raterelative to the respective removal rate of the second material.

Example 10. The method of example 9, wherein moving the substratethrough the gas cluster ion beam includes moving the substrate in theplane of the major surface.

Example 11. The method of example 1, wherein the feature is an openingwithin a patterned first layer that is disposed over the major surface,wherein the sidewalls of the opening form the sidewalls of the feature,wherein the width of the feature along the etch direction is a width ofthe opening between opposite sidewalls of the opening along the etchdirection, and wherein changing the width of the feature along a etchdirection increases the width of the opening along the etch direction.

Example 12. The method of example ii, wherein the feature is adjacent toa second opening within the first layer, the second opening beingpatterned simultaneously with the feature using a photolithographytechnique; wherein, along the etch direction, a dimension of the firstlayer between a sidewall of the feature and the adjacent sidewall of thesecond opening is greater than or equal to a resolution limit of thephotolithography technique; and wherein changing the width of thefeature along the etch direction reduces the dimension of the firstlayer along the etch direction between a sidewall of the feature and theadjacent sidewall of the second opening to be less than the resolutionlimit of the photolithography technique.

Example 13. The method of example 1, wherein the feature is a constructwithin a patterned first layer that is disposed over the major surface,the first layer being patterned using a photolithography technique,wherein the sidewalls of the construct form the sidewalls of thefeature, wherein the width of the feature along the etch direction is awidth of the construct between opposing sidewalls of the construct alongthe first direction, the width of the construct being greater than orequal to a resolution limit of the photolithography technique, whereinchanging the width of the feature along the etch direction reduces thewidth of the feature along the etch direction to less than theresolution limit of the photolithography technique.

Example 14. The method of example 1, wherein the feature is within apatterned first layer that is disposed over the major surface, the firstlayer being a hard mask including spin-on carbon, or silicon oxide, orsilicon nitride, or silicon anti-reflective coating, or titaniumnitride, or a metal, or a metal oxide, or a combination thereof.

Example 15. A method of processing a substrate includes loading thesubstrate on a substrate holder, the substrate including a major surfaceand a plurality of parallel lines disposed over the major surface; andexposing the plurality of parallel lines to a gas cluster ion beamoriented in a beam direction, the beam direction having an orthogonalprojection onto the major surface, the orthogonal projection beingoriented in an etch direction, wherein the plurality of parallel linesare parallel with the etch direction.

Example 16. The method of example 15, wherein the exposing causes asmoothing of the surfaces of the plurality of parallel lines.

Example 17. The method of example 15, wherein the exposing descums theplurality of parallel lines.

Example 18. The method of example 15, wherein exposing the plurality ofparallel lines to a gas cluster ion beam includes: loading the substrateon the substrate holder of a scanning apparatus; and orienting, usingthe scanning apparatus, the substrate relative to the gas cluster ionbeam by tilting the substrate at a selected tilt angle, the tilt anglebeing the angle formed by the beam direction and a line normal to themajor surface; and rotating the substrate about an axis normal to themajor surface, wherein the rotation orients the parallel lines in theetch direction; maintaining the substrate at a fixed orientationrelative to the gas cluster ion beam; selecting a set of gas cluster ionbeam parameters; and moving the substrate through the gas cluster ionbeam with the selected set of gas cluster ion beam parameters.

Example 19. The method of example 18, wherein the gas cluster ion beamprovides a target dose between 10¹¹ cm⁻² to 10¹⁶ cm⁻², and the selectedtilt angle has a magnitude between 55° and 85°.

Example 20. The method of example 15, wherein the plurality of parallellines includes lines having a core structure including a first materialand a sidewall structure including a second material, the secondmaterial being different from the first material.

Example 21. A method of processing a substrate includes loading thesubstrate on a substrate holder, the substrate including a majorsurface, a first feature disposed over the major surface at a firstlocation, and a second feature disposed over the major surface at asecond location; exposing the first feature to a first gas cluster ionbeam with a first process parameter; and exposing the second feature toa second gas cluster ion beam with a second process parameter, the firstprocess parameter being different from the second process parameter.

Example 22. The method of example 21, further including selecting thefirst process parameter and the second process parameter based onlocation specific data of a metric of the first feature and the secondfeature.

Example 23. The method of example 22, wherein the first processparameter and the second process parameter are selected based on:receiving location specific data of the metric of the first feature andthe second feature, receiving a function relating the metric to a valueof a process control parameter, wherein the first process parameter andthe second process parameter are values of the control processparameter, and using the location specific data and the function,calculating the first process parameter and the second processparameter.

Example 24. The method of example 23, wherein the control processparameter is a subset of a process parameter set including gas clusterion beam dose, tilt angle, twist angle, and dwell time.

Example 25. The method of example 22, wherein exposing the first featureand exposing the second feature includes: selecting a scan trajectory,the scan trajectory including the first location and the secondlocation; moving the substrate continuously along a scan trajectoryusing a scanning apparatus; and changing the process along the scantrajectory by selecting the first process parameter and the secondprocess parameter based on the location specific data.

Example 26. The method of example 25, wherein the first processparameter includes a first twist angle and the second process parameterincludes a second twist angle, and wherein the difference between thefirst twist angle and the second twist angle is less than or equal to180 degrees.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method of processing a substrate, the methodcomprising: loading the substrate on a substrate holder, the substratecomprising a major surface, and a feature disposed over the majorsurface, the feature having a first width along an etch direction andexposing portions of the major surface; and changing the first width ofthe feature to a second width along the etch direction by etching afirst portion of sidewalls of the feature with a ion beam oriented alonga beam direction.
 2. The method of claim 1, wherein the etch directionis along the orthogonal projection of the beam direction on the majorsurface so that the ion beam is inclined at a tilt angle with a normalto the major surface or the etch direction is parallel to the majorsurface and perpendicular to the sidewalls.
 3. The method of claim 1,wherein the substrate is oriented in a first orientation relative to theetch direction while changing the first width, wherein the methodfurther comprising rotating the substrate to a second orientationrelative to the etch direction, and changing the second width of thefeature to a third width along the etch direction by etching a secondportion of the sidewalls of the feature with the ion beam oriented alongthe beam direction.
 4. The method of claim 1, further comprising:loading the substrate on the substrate holder of a scanning apparatus;and orienting, using the scanning apparatus, the substrate relative tothe ion beam by tilting the substrate at a selected tilt angle, the tiltangle being the angle formed by the ion beam and a line normal to themajor surface; and rotating the substrate about an axis normal to themajor surface, wherein the rotation orients a reference axis in themajor surface to form a selected twist angle between the reference axisand a line parallel with the etch direction.
 5. The method of claim 4,wherein the tilt angle is selected for the ion beam to impinge on aboundary between the exposed portion of the major surface and a sidewallof the feature, and wherein the tilt angle is selected to reduce thedifference between the tilt angle and a right angle.
 6. The method ofclaim 1, wherein the feature is within a patterned first layer that isdisposed over the major surface, the major surface comprising a secondlayer, wherein the first layer comprises a first material, and whereinthe second layer comprises a second material; and wherein changing thewidth of the feature along the etch direction comprises maintaining thesubstrate at a fixed orientation relative to the ion beam; exposing atarget area of the substrate to a target dose of cluster impacts bymoving the substrate through the ion beam; and removing the firstmaterial at a faster removal rate relative to the respective removalrate of the second material.
 7. The method of claim 6, wherein movingthe substrate through the ion beam comprises moving the substrate in theplane of the major surface.
 8. The method of claim 1, wherein thefeature is an opening within a patterned first layer that is disposedover the major surface, wherein the sidewalls of the opening form thesidewalls of the feature, wherein the width of the feature along theetch direction is a width of the opening between opposite sidewalls ofthe opening along the etch direction, and wherein changing the width ofthe feature along a etch direction increases the width of the openingalong the etch direction.
 9. The method of claim 8, wherein the featureis adjacent to a second opening within the first layer, the secondopening being patterned simultaneously with the feature using aphotolithography technique; wherein, along the etch direction, adimension of the first layer between a sidewall of the feature and theadjacent sidewall of the second opening is greater than or equal to aresolution limit of the photolithography technique; and wherein changingthe width of the feature along the etch direction reduces the dimensionof the first layer along the etch direction between a sidewall of thefeature and the adjacent sidewall of the second opening to be less thanthe resolution limit of the photolithography technique.
 10. The methodof claim 1, wherein the feature is a construct within a patterned firstlayer that is disposed over the major surface, the first layer beingpatterned using a photolithography technique, wherein the sidewalls ofthe construct form the sidewalls of the feature, wherein the width ofthe feature along the etch direction is a width of the construct betweenopposing sidewalls of the construct along the etch direction, the widthof the construct being greater than or equal to a resolution limit ofthe photolithography technique, wherein changing the width of thefeature along the etch direction reduces the width of the feature alongthe etch direction to less than the resolution limit of thephotolithography technique.
 11. The method of claim 1, wherein thefeature is within a patterned first layer that is disposed over themajor surface, the first layer being a hard mask comprising spin-oncarbon, or silicon oxide, or silicon nitride, or silicon anti-reflectivecoating, or titanium nitride, or a metal, or a metal oxide, or acombination thereof.
 12. A method of processing a substrate, the methodcomprising: loading the substrate on a substrate holder, the substratecomprising a major surface and a plurality of parallel lines disposedover the major surface; and exposing the plurality of parallel lines toa ion beam oriented in a beam direction, the beam direction having anorthogonal projection onto the major surface, the orthogonal projectionbeing oriented in an etch direction, wherein the plurality of parallellines are parallel with the etch direction.
 13. The method of claim 12,wherein the exposing causes a smoothing of the surfaces of the pluralityof parallel lines.
 14. The method of claim 12, wherein the exposingdescums the plurality of parallel lines.
 15. The method of claim 12,wherein exposing the plurality of parallel lines to a ion beamcomprises: loading the substrate on the substrate holder of a scanningapparatus; and orienting, using the scanning apparatus, the substraterelative to the ion beam by tilting the substrate at a selected tiltangle, the tilt angle being the angle formed by the beam direction and aline normal to the major surface; and rotating the substrate about anaxis normal to the major surface, wherein the rotation orients theparallel lines in the etch direction; maintaining the substrate at afixed orientation relative to the ion beam; selecting a set of ion beamparameters; and moving the substrate through the ion beam with theselected set of ion beam parameters.
 16. The method of claim 15, whereinthe ion beam provides a target dose between 10¹¹ 10⁻² to 10¹⁶ cm⁻² andthe selected tilt angle has a magnitude between 55° and 85°.
 17. Themethod of claim 12, wherein the plurality of parallel lines compriseslines having a core structure comprising a first material and a sidewallstructure comprising a second material, the second material beingdifferent from the first material.
 18. A method of processing asubstrate, the method comprising: loading the substrate on a substrateholder, the substrate comprising a major surface, a first featuredisposed over the major surface at a first location, and a secondfeature disposed over the major surface at a second location; exposingthe first feature to a first ion beam with a first process parameter;and exposing the second feature to a second ion beam with a secondprocess parameter, the first process parameter being different from thesecond process parameter.
 19. The method of claim 18, further comprisingselecting the first process parameter and the second process parameterbased on location specific data of a metric of the first feature and thesecond feature.
 20. The method of claim 19, wherein the first processparameter and the second process parameter are selected based on:receiving location specific data of the metric of the first feature andthe second feature, receiving a function relating the metric to a valueof a process control parameter, wherein the first process parameter andthe second process parameter are values of the control processparameter, and using the location specific data and the function,calculating the first process parameter and the second processparameter.
 21. The method of claim 20, wherein the control processparameter is a subset of a process parameter set comprising ion beamdose, tilt angle, twist angle, and dwell time.
 22. The method of claim19, wherein exposing the first feature and exposing the second featurecomprises: selecting a scan trajectory, the scan trajectory comprisingthe first location and the second location; moving the substratecontinuously along a scan trajectory using a scanning apparatus; andchanging the process along the scan trajectory by selecting the firstprocess parameter and the second process parameter based on the locationspecific data.